Howdy Frank,
You have a parking meter question and I am currently working on shelves to hold a few of my meters.

That bracket is very interesting. I have never seen one like it with any of the meters I have. To make a guess I would say it goes inside the coin vault and is held down with the same bolt that tightens the mounting wedges. That would be my best guess.
Good luck and may God bless us all,
Mike